ubuntu-phone team mailing list archive

[Jamie Strandboge <jamie@xxxxxxxxxx>]

On 06/02/2015 02:10 PM, Frans Schreuder wrote:
> Dear Ubuntu-phone mailing list,
> 
> I have spent a few weeks developing an offline routing / navigation
> application (LGPL) based on openstreetmaps / libosmscout.
> I want to publish the app in the Ubuntu App Store, but I am facing a
> problem: I need read access on a location on the SD card. I will explain
> why.
> 
...

> For now there are no good apparmor rules that matches the need of this
> application,

This is a complicated topic and currently app-access to the SD card is not fully
implemented. This has been discussed in the past and the main points are:

 * we don't want to allow a shared storage area like <SD CARD>/freeforall
   because that breaks application isolation
 * we could try to do something like:
     owner <SD CARD>/<USER>/<PKGNAME>/** rwk
   similar to the app-specific directories in /home, but that only works well
   with Linux filesystems (eg, ext4) because some filesystems may not support
   case-sensitivity, separate UIDs (for multiuser systems) or long filenames
 * Most things in Ubuntu Touch aren't aware of the SD CARD and the user
   experiences have not been defined

Because of this, only a couple of apps have special exceptions that grant them
access to the filesystem.

> Picture read could be possible, however it needs the maps
> to be placed in <SD_CARD>/Pictures/osmscout. That is an ugly solution,
> but it works.
It does work in the sense that your app now has access to the folder, but it
almost certainly doesn't work in the gallery, mediascanner, etc that have to
deal with GBs of data that are in a subfolder that it scans for updates. Those
apps would have to be updated to ignore the osmscout subfolder, which is even
uglier.


> Another solution is to set the app as unconfined, and use the location
> <SD_CARD>/Maps/osmscout. However this is not the solution to allow for
> any app, I think this app really adds value to the Ubuntu phone.
> Would it be possible to create an app-specific rule that allows (Read,
> and maybe later Write) access to <SD_CARD>/Maps/? Or otherwise to allow
> this app to be published as unconfined?
> 
There is no reason to run it unconfined when an app-specific directory could be
used instead. As far as exceptions go, this is the cleanest solution because
only your app would have access to this directory. Because of the
case-insensitivity, you would need to do something like this:
  read_path: [
    "/media/*/*/[Mm][Aa][Pp][Ss]/"
  ]

However, if you add that, what happens if the user has an Ubuntu Touch device
that doesn't have an SD Card (eg, the reference Nexus 4)? AIUI, most new devices
have a lot more storage and many are foregoing SD card support altogether.


Now, this doesn't deal with all the other problems with non-Linux filesystems on
the SD CARD.

I've included Thomas Voß in this email because he may have more information on
the current status. Thomas (please forward if someone else knows),
 * what is the current status of SD CARD access by apps, especially wrt
   multiuser (UID mappings), case-insensitivity and short filenames? Is there a
   roadmap?
 * is there a better way to handle map data? It seems like Frans is having to
   deal with a lot of difficulties here with pregenerating map data and getting
   it onto the SD Card. Are there plans for a maps service or something?
 * should we create a restricted 'maps' policy group that allows '~/Maps' and
   '/media/.../Maps' like how the gallery current owns '~/Pictures'? The
   question then is, who is the actual owner of Maps (ie, osmscout isn't like
   gallery)?

-- 
Jamie Strandboge             | http://www.ubuntu.com

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